Electrical rotating machines are installed, as power sources, in various apparatuses, and their applications to vehicles include, for example, a power source of an electric vehicle when installed alone in the vehicle or a power source of a hybrid electric vehicle to operate in association with an internal combustion engine. Hybrid electric vehicles are specifically expected to increase mechanical efficiency of power transmission, so there is a need for a torque high enough to enhance acceleration performance and performance to clear differences in level.
In particular, sometimes, the hybrids, utilizing, for example, a power transmission path which sequences an internal combustion engine, an electrical rotating machine and traction wheels in series (a serial sequence type), allow the traction wheels to spin entirely on the electrical rotating machine and extend range of the vehicle by re-charging a power source battery for the electrical rotating machine after converting power of the internal combustion engine into electric energy, a so-called “range extender” system.
Moreover, in some electrical rotating machines, in order to provide big output or big torque with compact construction, operation at high-efficient rotation by using permanent magnets is conducted.
Incidentally, energy flow through a power transmission path which requires conversion from mechanical energy to electrical energy results in massive conversion losses and prolonging the power transmission path or prolonged energy path results in a drop in energy transmission efficiency. Range extender system, for example, allows its electrical rotating machine to operate by controlling supply of electrical energy to and/or discharge of electrical energy from its power source battery because the electrical rotating machine is situated between the rotation of traction wheels and the rotation of an internal combustion engine. Thus, in the range extender system, the prolonged energy path in addition to energy conversion loss brought about by requiring energy conversion between mechanical energy and electrical energy becomes one of causes for a drop in energy transmission efficiency.
Meanwhile, JP2013-208015A (Patent Literature 1), for example, describes an electrical rotating machine with double-rotors inside a stator and makes it known to couple rotating shafts for the rotors to the side of traction wheels and the side of an internal combustion engine, respectively.
Even such electrical rotating machine is allowed to conduct high efficient rotation by use of permanent magnets on the rotor side in order to provide big output or big torque with compact construction, resulting in a cost increase if, on this occasion, rare and precious permanent magnets such as neodymium magnets are used to obtain high power magnetic force.
Using electromagnets in place of permanent magnets and supplying electric power to the electromagnets on the rotor side require, for example, slip rings or the like for supply of electric power to coils and an inverter, resulting in complicated construction to cause an increase in the number of components, leading to a cost increase.